-89 Ranger overheating...or is it?

JukkaK · Sep 12, 2018

Hi,

I have a -89 Ranger with 2.9 EFI and automatic transmission, it has about 100k miles on it. When I got it few months ago I noticed right away that the temp gauge goes almost over, and sometimes a little over, the 'NORM' range. I immediately replaced the thermostat and made sure that the cooling system is full and the radiator isn't full of dirt outside, still the same thing.

I've been driving it for three months like this now. I believe that it is bad temp sensor for the gauge, you know, the sensor with one wire going in it. Is there a known resistance for a good temp sensor? What are the ohms readings that tells me that it's bad for sure? Is the water pump known to go bad in these? I noticed that the coolant was dirty and old when I replaced the thermostat, that won't do any good for the water pump over time that's for sure.

Thank you!

- Jukka

cocoasranger · Sep 13, 2018

I also have a 1989 2.9l Ranger. The temp. sensors are known to degrade over time. They are inexpensive and easy to replace; just screw a new one in. Mine had always barely registered on the gauge, even in hot weather. After a new sensor was installed the gauge reads accurately and stays at the "N" in normal after the engine reaches operating temperature.

killswitch21 · Sep 13, 2018

cocoasranger said:
I also have a 1989 2.9l Ranger. The temp. sensors are known to degrade over time. They are inexpensive and easy to replace; just screw a new one in. Mine had always barely registered on the gauge, even in hot weather. After a new sensor was installed the gauge reads accurately and stays at the "N" in normal after the engine reaches operating temperature.

This!

Same deal in my 1990 2.9L Ranger. Temp gauge never really moved at all. I replaced that sensor(it is cheap and easy) and now it sits at the O or R of normal. I can tell when the thermostat opens because it falls back from the R to the O.

To be fair, I did replace my radiator because of a crack, fan, fan clutch, thermostat, upper hose, and the sensors. Cools like a champ now

JukkaK · Sep 13, 2018

I'll replace the sensor. Alltough the parts are not that easy to get and are not nescessarilly inexpencive here in Finland.

But just to put the information forward I actually measured the resistance of the sensor yesterday morning. Readings were 500ohms with a stone cold engine and 35ohms after I drove to work, the gauge was still barely in the NORMAL range though. I believe it should be more than 500ohms when cold but I'm not sure. I will report the readings with the new sensor when I get it.

JukkaK · Sep 14, 2018

Got the new sensor installed. The weird thing is that, while the gauge seems to be in the middle of the NORMAL range now, the ohms reading of the hot sensor is pretty much the same as before. Cold sensor reading is about 280ohms

I can see the thermostat opening and closing by looking at the gauge, it goes a little bit lower when the thermostat opens and then a little bit higher again when the thermostat closes but it newer goes in the high side of the NORMAL range now.

My multimeter is a cheap one so I'm not 100% sure about its accuracy.

4x4junkie · Sep 14, 2018

I think you're fine.

The fact you're able to observe the gauge drop a bit when the thermostat opens seems indicative things are working as they should.

Just keep the coolant clean & fresh (change it about every 2-3 years regardless of mileage) and you should be good.

Welcome to TRS. :beer:

-89 Ranger overheating...or is it?

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